(1) Field of the Invention
This invention relates to provision of an improvement in a center mechanism for use in a tire press, particularly a standing well type center mechanism.
(2) Description of the Prior Art
There has been known a tire press for molding and vulcanizing a green tire which comprises a lower mold equipped with a heat source, an upper mold also equipped with a heat source and capable of being opened and closed relative to the lower mold, and a molding bladder capable of being let in and out of a well disposed in the center of the lower mold, and in which a heating and pressurizing medium (steam or the like) is supplied into the bladder to mold and vulcanize the green tire, as for instance disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 61-219606 (1986).
Particularly, the tire press in which the molding bladder is contained in an upright cylinderical form without being folded in the well, as disclosed in the above-mentioned patent application, is called the standing well post type and is becoming the mainstream type of tire press in view of the fact that, in this type, the durability of the molding bladder, formed of rubber or other elastic material, is not degraded.
It is necesssary for the above-mentioned molding bladder to be affixed to the inner surface of the green tire, or be released from the inner surface of the green tire and contained in the upright cylindrical form in the well, or be contracted or expanded in shape according to the operations of setting the green tire in position, shaping the tire and vulcanizing and molding the tire. For carrying out these motions, therefore, a center mechanism comprising a well disposed in the center of the lower mold is used.
In general, as disclosed in the above-mentioned Japanese Patent Application Laid-Open (KOKAI) No. 61-219606 (1986), the center mechanism comprises a bladder well provided with a lower bead ring at the upper end thereof, and upper clamp right assembly for holding the upper end of a molding bladder, and a lower clamp ring assembly for holding the lower end of the molding bladder, the three members being vertically liftable independently of each other. The bladder well, the upper clamp ring assembly and the lower clamp ring assembly are lifted up or down to respective required positions, thereby bringing the bladder into operative movements, and a heating and pressurizing medium such as high-temperature high-pressure steam is supplied into the bladder by heating and pressurizing medium supply means provided in the center mechanism. The upward and downward motions of each of the above-mentioned members required are carried out, without exception, by lift means comprising an oil cylinder and a piston rod disposed in the cylinder, as is know.
The center mechanism of the type as mentioned above involves the following problems.
At the time of vulcanization and molding of the green tire, a large quantity of high-temperature high-pressure steam or the like is supplied continuously into the bladder, and the heat hereof has effects on the entire body of the center mechanism.
The oil cylinders, naturally, are low in resistance to heat and are easily changed in properties when heated. Even if a strict seal structure is applied to the oil cylinders, there remains a high possibility of seal deterioration or leak troubles. To protect the hydraulic oil from heat, therefore, it is necessary to use a large number of pieces of heat insulator for each of the members and at joint and lap portions of the members. The use of the heat insulators, accompanied by a complicated construction and a short lifetime of heat-resistant material, leads to the need for constant inspection and repair.
Furthermore, assured separation of the component parts by heat insulator involves an increase in the number of component parts required. Disposing the oil cylinders for lift operations at locations remote from a heat source leads to an increase in the vertical overall length of the center mechanism, and requires a modification in the design of, for instance, a base on which to mount the center mechanism.
For holding, for instance, the lower clamp ring assembly in a predetermined position against the high-pressure steam supplied into the bladder, the use of the oil cylinder alone is insufficient in capability, and a separate clamp mechanism based on mechanical means is therefore required. Such a means conventionally used comprises lock grooves formed in the peripheral surface of the guide rod or piston rod located in the center of the press, and a pair of locking levers disposed on opposite sides of the guide rod or piston rod, the levers capable of being engaged with the disengaged from the lock grooves. The pair of locking levers are turned by converting a vertical motion into a rotational motion by a slide guide mechanism, and transmitting the rotation to the locking levers in tune through a pinion gear or the like, thereby opening or closing the levers. This system requires a large number of component parts, complicates the design in the limited well, and has a high possibility of troubles occurring therein.